Patio style umbrellas that are particularly large can be difficult to operate due to the substantial force needed to raise the relatively heavy canopy to an open position. A crank and gear reduction mechanism can be used to reduce the force, but such manual mechanisms can be tedious to use due to the time it takes to crank the umbrella open and closed. The cranking action can also apply an undesirable rotational moment on the umbrella's mast, wherein the rotational moment urges the canopy to twirl back and forth with each revolution of the crank.
As an alternative, U.S. Pat. No. 6,058,951 discloses a motor powered umbrella where a motorized mechanism pulls on a set of spokes or linkage that lifts the canopy to its open, raised position. As explained in column 3, lines 46-48 of the '951 patent, the weight of the canopy can later be used in returning the umbrella back down to its closed position. The motorized mechanism, of course, requires a source of electrical power that, unfortunately, might not always be readily available.
Another alternate design is disclosed in U.S. Pat. No. 6,082,383. Instead of purely raising the entire canopy to the open position, the canopy's outer perimeter rises while a central portion actually descends. This reduces the total distance that the umbrella's center of gravity must travel, thus reducing the energy and force required to operate the umbrella. This design, unfortunately, requires a long slot (item 22 of the '383 patent) in the umbrella's mast, and such a slot is not easily manufacturable by high production means. Moreover, such a slot can weaken the mast.
Consequently, there still is a need for an umbrella actuator that overcomes the drawbacks of existing mechanisms.